This invention relates generally to electromagnetic locks which are employed in connection with doors for controlling egress and/or access through the door. More particularly, the present invention relates to electromagnetic lock systems which are adapted to provide for delayed egress through an exit door and/or a security alarm for monitoring egress.
Electromagnetic locks have been employed for a number of exit door/emergency door applications so as to provide an effective and reliable means for locking the door while also permitting egress through the door in emergency situations. A number of electromagnetic lock systems have incorporated a time delay implemented by various devices. The time delay systems effectively delay unlocking of the electromagnetic lock for a pre-established time interval, such as 15 or 30 seconds, to enhance security and control egress from a secured enclosure. A number of electromagnetic lock systems have also incorporated various devices for activating an alarm when an attempt is made to egress through the associated exit or emergency door. In addition, a number of electromagnetic lock systems incorporate devices for releasing time electromagnetic lock in case of fire or other emergency conditions.
Emanual L. Logan, Jr. et al, U.S. Pat. No. 4,720,128 discloses an electromagnetic emergency exit door lock implementing a time delay for egress through a doorway. A switch is mounted adjacent to the electromagnet and the switch is operated by a switch operator mounted on the door. The switch provides a signal which indicates that an attempt is being made to open the door. The signal is used to sound an alarm or start a time delay release of the electromagnetic lock. The switch comprises a plunger, a magnet and a hall cell which are located within a compartment disposed beside the electromagnetic. When the door is closed and locked, a striker on the door engages the plunger of the switch. When a person in the enclosure presses either a panic bar or the inside surface of the door so as to force the door to move slightly, the plunger moves to displace a magnet from the hall cell and generate a signal indicating someone is attempting to leave the enclosure.
Additional electromagnetic lock systems to which the invention relates are set forth by patentee and U.S. Pat. Nos. in the Table below.
______________________________________ Patentee U.S. Pat. No. ______________________________________ Frolov 4,957,316 McFadden 4,487,439 Logan 4,324,425 Logan 4,257,631 ______________________________________